Seminar:
Cracking the code of corrosion in concrete

The history of cathodic protection is more than 200 years, but the history of cathodic protection of reinforced structures in Denmark only dates back to the late 1980´es.

Moreover, it was not before 2003, cathodic protection of reinforced structures became acknowledged as a repair strategy by the Danish road directorate that is became widely used, not the least for protection of our Danish maritime structures.

The presentation will present the first cathodic protection projects and the reinforced concrete repair strategy, jointly with works in international standards on cathodic protection and the certification schemes available.

How will the protection current be distributed along the rebar in concrete CP installations? This is a pivotal – and one of the most relevant – questions to have in mind when designing cathodic protection installations. An unexpected current distribution can result in either reduced polarization or damage to the rebar but also severely damage the concrete or anode material if not discovered and remediated in time.

There are a number of factors that will influence the current distribution, and knowing which ones are critical or less critical to consider and control is essential in the process of designing a proper CP system for concrete applications.

This presentation will provide an overview of some of the general current distribution considerations applied in the design stage of CCP systems for concrete and it will also highlight the importance of other – often less considered – factors and their potential impact through practical field examples. More factors and concerns are likewise mentioned as a basis for common , interesting and hopefully enlightening discussions.

The presentation provides insight into how the understanding of corrosion initiation and chloride intrusion in reinforced concrete structures has influenced the concrete specifications for the Great Belt Link and other major infrastructure projects in Denmark and abroad. The presentation will take the audience through the history of the development of the requirements for concrete durability in aggressive, chloride-containing environments that we know today. It is a journey that starts with simple mathematical models and moves through advanced mathematics to be able to handle the signals that the collected data gave. The journey ends in our modern, nuanced requirements to make concrete sufficiently resistant to protect the reinforcement against corrosion for up to 120 years (and sometimes more) – requirements that are still under development, differentiation, and implementation.

The presentation focusses on the main limiting factors for designing concrete structures with very long service lives: general chloride ingress and cracks. The limitations from these factors and examples of overcoming these limitations are presented mainly by examples from illustrative structures, mainly the Great Belt Bridge. It is shown that the main problems from chloride ingress are very local but solving these problems by usual methods (increasing concrete cover and improving concrete composition) can be difficult, and presented alternative methods might be more relevant. Regarding cracks results from high performance concretes indicate that the actual design criteria might be too optimistic for preventing corrosion initiation, but the corrosion might propagate much slower than expected.

The right maintenance of concrete structures by implementation of sensors will be vital in the near future. That is why the proper use of the right sensors can be essential for extending operation lifetime of the structure and therefore the presentation will take a brief historical background for sensors and point out the advantages using different types of sensors. The presentation will also discuss the challenge of getting real time monitoring and how to use AI for quickly analyzing large amounts of data to identify patterns that can provide insights that support strategic decisions. Finally, it gives a status for the CorroSense project.

Reinforced concrete structures, particularly in marine environments, are vulnerable to premature corrosion initiation due to chloride ingress. Especially in the splash zone, where the fluctuating water level challenges traditional cathodic protection methods. In a laboratory setup, it is investigated whether the corrosion initiation can be delayed or prevented, by applying cathodic protection from the beginning of a structure’s lifespan. The results demonstrated that applying low levels of cathodic current influenced the timing and extent of corrosion initiation in some specimens. These findings suggest that early application of impressed current cathodic protection may delay corrosion initiation in concrete structures.

The work described in this presentation involves initial fundamental work of controlling current flow through specially formulated controlled current output ICCP anodes in a concrete slab. The results were very encouraging suggesting that such anodes can distribute the current around the steel reinforcement much more evenly and avoid short-circuiting by not exceeding the predetermined current output. Modelling was then used to successfully prove the concept. An example of an ICCP field design is described and discussed.